氘化对KH2PO4晶体微观缺陷影响的正电子湮没研究∗

摘要

Deuterated potassium dihydrogen phosphate (K(DxH1−x) 2PO4) crystals with different deuteration levels (x=0, 0.51, 0.85) were grown by conventional cooling method from deuterated solutions at Shandong University. Positron annihilation spectroscopy has been widely used to the study on micro-defects of semiconductors and other materials, which is very sensitive to the crystal structure, defect types, defect concentrations, and so on. In this paper, positron annihilation spectroscopies (positron annihilation lifetime spectroscopy and Doppler broadening spectroscopy), combined with X-ray diffraction (XRD) are used to investigate micro-defects characterization in K(DxH1−x) 2PO4 crystals. Influences of deuteration degree on the crystal structure characteristics, defect types and concentrations are discussed. It can be concluded from XRD experiments that the lattice parameters of a and b increase with the increase in deuteration levels, while no obvious change occurs on the lattice parameter c. KH2PO4(KDP) crystals at low deuteration level and high deuteration level could be regarded as low deuterium-doped KDP crystal and low hydrogen-doped DKDP crystal respectively. It is indicated that the higher the replacement ratio in the crystals, the weaker the diffraction peak they show. Positron annihilation lifetimes increase clearly in the highly-deuterated KDP crystals. It is found that neutral interstitial defects and oxygen defects in the KDP crystal increase with increasing deuteration degree. And these types of defects can be attributed to lattice distortion effect. From positron annihilation lifetime results we can arrive at another conclusion that the compound defects will form and defects concentration is declined, when hydrogen vacancies, K vacancies and substitutional impurity defects continue to react by means of association reactions. These phenomena suggest that high deuteration plays a significant role in promoting association reaction of internal defects in the crystals. Furthermore, the polymerization reaction of the clusters and micro-cavities continue to occur, therefore defect concentrations will show a constant decrease. Doppler broadening spectra show that the internal defects in the crystals increase integrally with an increase of deuteration level;this agrees well with the results of positron annihilation lifetime. Moreover, Doppler broadening spectra indicate that the proportional change of these defects is synchronous and consistent with the actuality. To sum up, our experimental results suggest that the defect reaction is weak in low degree of KDP crystal deuteration growth (less than 50%), while reaction is enhanced in the high degree of deuteration growth (higher than 50%).%采用传统降温法从不同程度氘化(x=0,0.51,0.85)的生长溶液中生长氘化KH2PO4(KDP)晶体,利用正电子湮没技术(正电子寿命谱和多普勒展宽谱)、结合X射线衍射谱(XRD)结构分析,对KDP晶体氘化生长的微观缺陷进行了研究,讨论了氘化程度对晶体内部微观结构特性、缺陷类型和浓度的影响. XRD结果显示晶胞参数a, b值随氘含量的增加而增加, c值无明显变化；正电子寿命谱结果发现随着氘化浓度的提高, KDP晶体内部中性填隙缺陷以及氧缺陷不断增加,引起晶体晶格畸变；氢空位、K空位、杂质替位缺陷不断发生缔合反应形成复合缺陷,缺陷浓度不断减少；团簇、微空洞等大尺寸缺陷也在不断发生聚合反应,缺陷浓度表现为不断减少.多普勒实验结果表明随着氘化程度的提升,晶体内部各类缺陷表现为同步变化.实验结果表明, KDP晶体在低浓度氘化生长(50%以内)下缺陷反应较弱,而在高浓度氘化(50%以上)下的缺陷反应显著增强.